Tire forming method and tire forming mold

ABSTRACT

The invention provides a tire forming mold and a tire forming method such that letters and lines of a formed tire can be clearly displayed in the case of forming the tire in which the letters and the lines having different colors are formed in a side wall portion. In a tire forming mold for vulcanization forming by being brought into contact with an outer surface of a tire which is provided with a side rubber layer  19  of a first color arranged in an outer side of a carcass ply  13  of a side wall portion  11 , a white rubber layer  20  of a second color arranged in adjacent to an outer side of the side rubber layer  19 , and a cover rubber  21  of the first color arranged in adjacent to an outer side of the white rubber layer  20 , the tire forming mold comprises a rubber inflow portion  30  for forming a protrusion portion  31  in an outer surface of the tire by inflowing the white rubber layer  20  and the cover rubber  21 , in the contact surface with the tire, wherein a cross sectional shape of the rubber inflow portion  30  is constructed by a neck portion  30   b  extending from an inflow port  30   a , and a head portion  30   c  enlarged from the neck portion  30   b.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tire forming method and a tireforming mold, and more particularly to a forming method of a tire inwhich letters and lines having different colors are formed in a sidewall portion, and a tire forming mold.

2. Description of the Related Art

Conventionally, for the purpose of enhancing a fashion property or thelike, there has been known a pneumatic tire (hereinafter, sometimesreferred simply to as a tire) in which letters and lines havingdifferent colors are formed in a side wall portion. Particularly, thepneumatic tire in which the letters and lines of a white rubber areformed on an outer surface of the side wall portion may be called awhite letter tire, a white line tire or the like.

Japanese Unexamined Patent Publication No. 5-8612 describes a formingmethod of a pneumatic tire in which an embossed mark including a whiteletter is formed in a side wall portion of a tire. Specifically, a greentire is formed by burying and attaching a white rubber body in a concaveportion provided in a side wall rubber body for forming a side wallportion, and laminating a thin and black rubber sheet on a surfacethereof, and the white rubber body is exposed by pressing a metal moldhaving a concavo-convex portion coinciding with a pattern shape such asthe letter to the side wall portion at a time of vulcanization forming,applying a buff treatment to a convex portion of the concavo-convexsurface formed in the side wall portion, and removing the black rubbersheet.

Patent document 1: Japanese Unexamined Patent Publication No. 5-8612

SUMMARY OF THE INVENTION

FIGS. 9A to 9C show a state in which a metal mold is pressed to a sidewall portion, and a concavo-convex surface is formed in the side wallportion. As shown in FIG. 9A, when a metal mold 3 is pressed to a sidewall portion S in which a white rubber W and a black cover rubber B arelaminated, from an outer side, as shown in FIG. 9B, the white rubber Wand the black cover rubber B flow into a concave portion of the metalmold 3, so that a convex portion is formed on a surface of the side wallportion S. The white rubber W can be exposed to the surface by buffing aleading end of the convex portion formed as mentioned above on a buffsurface shown by a broken line in FIG. 9C.

However, there is a case that an amount of the internal white rubber Wbecomes less than a desired amount in some formed convex portion, forexample, a lower convex portion in two convex portions shown in FIGS. 9Band 9C. Even if the convex portion mentioned above is buff treated,there is a case that a lot of black cover rubber B is left, so that theletters and the line widths such as the white letters and the whitelines get out of order and are not clearly displayed. It is thought thatthis is caused by a case that the concave portion of the metal mold istapered, so that the white rubber W can not flow into the concaveportion appropriately.

The present invention has been made in view of the above circumstances,and an object thereof is to provide a tire forming mold and a tireforming method such that letters and lines of a formed tire can beclearly displayed in the case of forming the tire in which the lettersand the lines having different colors are formed in a side wall portion.

Means for Solving the Problems

The object mentioned above can be achieved by the present inventiondescribed as follows.

In other words, in accordance with the present invention, there isprovided a tire forming mold for vulcanization forming by being broughtinto contact with an outer surface of a tire which is provided with aside rubber layer of a first color arranged in an outer side of acarcass ply of a side wall portion, a different color rubber layer of asecond color arranged in adjacent to an outer side of the side rubberlayer, and a cover rubber layer of the first color arranged in adjacentto an outer side of the different color rubber layer, the tire formingmold comprising:

a rubber inflow portion for forming a protrusion portion in an outersurface of the tire by inflowing the different color rubber layer andthe cover rubber layer, in the contact surface with the tire, wherein

a cross sectional shape of the rubber inflow portion is constructed by aneck portion extending from an inflow port, and a head portion enlargedfrom the neck portion.

A description will be given of an operation and an effect of the tireforming mold having the structure mentioned above. The tire forming moldaccording to the present invention is structured such as tovulcanization form by being brought into contact with the outer surfaceof the tire provided with the side rubber layer of the first colorarranged in the outer side of the carcass ply of the side wall portion,the different color rubber layer of the second color arranged inadjacent to the outer side of the side rubber layer, and the coverrubber layer of the first color arranged in adjacent to the outer sideof the different color rubber layer, and can form the tire in which theletters and the lines having the different colors are formed in the sidewall portion. The tire forming mold according to the present inventionis provided with the rubber inflow portion in the contact surface withthe tire, and can form the protrusion portion on the outer surface ofthe tire by inflowing the different color rubber layer and the coverrubber layer. The cross sectional shape of the rubber inflow portion isconstructed by the neck portion extending from the inflow port, and thehead portion enlarged from the neck portion. As a result, the protrusionportion formed in the tire is formed such that the leading end portionis bulged. As mentioned above, since the rubber inflow portion is formedin such a manner as to be provided with the enlarged head portion fromthe neck portion, the rubber tends to flow into the head portion throughthe neck portion in comparison with the case of the conventionally knowntapered shape as shown in FIG. 9A to 9C, and the rubber flow of thedifferent color rubber layer in the neck portion becomes good.Accordingly, since the desired amount of different color rubber layerexists in the position formed by the neck portion of the rubber inflowportion, in the protrusion portion of the tire, the different colorrubber layer is exposed to the surface in the desired aspect by bufftreating at this position, and the letters and the lines of the tireafter being formed are clearly displayed.

In the tire forming mold in accordance with the present invention, it ispreferable that the head portion is formed into a round shape.

As long as the head portion is formed into the round shape, even if thehead portion is formed into the enlarged shape from the neck portion,the protrusion portion formed in the tire can be easily drawn off fromthe rubber inflow portion at a time of drawing off the tire from thetire forming mold after the vulcanization forming, and the protrusionportion less gets chipped. Further, in the case that the head portion isformed into the round shape, the different color rubber layer tends toflow into the head portion, so that the rubber flow of the neck portionbecomes better. As a result, the letters and the lines of the tire afterbeing formed can be more clearly displayed.

The object mentioned above can be achieved by the present inventiondescribed as follows.

In other words, in accordance with the present invention, there isprovided a tire forming method of vulcanization forming by arranging aside rubber layer of a first color in an outer side of a carcass ply ofa side wall portion, arranging a different color rubber layer of asecond color in adjacent to an outer side of the side rubber layer, andbringing an outer surface of a tire in which the cover rubber layer ofthe first color is arranged in adjacent to an outer side of thedifferent color rubber layer into contact with a tire forming mold,

wherein the tire forming mold is provided with a rubber inflow portionin a contact surface with the tire, and a cross sectional shape of therubber inflow portion is constructed by a neck portion extending from aninflow port, and a head portion enlarged from the neck portion, and

a protrusion portion is formed in the outer surface of the tire byinflowing the different color rubber layer and the cover rubber layerinto the rubber inflow portion.

The operation and the effect of the tire forming method having thestructure mentioned above have been already mentioned. According to thetire forming method of the present invention, the letters and the linesof the tire after being formed can be clearly displayed, in the case offorming the tire in which the letters and the lines having the differentcolors are formed in the side wall portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view schematically showing anexample of a tire forming mold according to the present invention;

FIG. 2 is a plan view of a tread mold portion;

FIG. 3 is an enlarged view of a substantial part of the tire formingmold;

FIGS. 4A and 4B are enlarged views of a substantial part of a tireforming mold according to another embodiment of the present invention;

FIG. 5 is a tire meridian cross sectional view schematically showing anexample of a pneumatic tire;

FIG. 6 is a substantial part cross sectional view showing a substantialpart of the pneumatic tire in an enlarged manner;

FIGS. 7A to 7C are explanatory views for explaining a tire formingmethod;

FIG. 8 is an enlarged view showing shapes of rubber inflow portions oftire forming molds according to an example and a comparative example;and

FIGS. 9A to 9C are explanatory views for explaining a conventional tireforming method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given below of an embodiment according to thepresent invention with reference to the accompanying drawings. FIG. 1 isa vertical cross sectional view schematically showing an example of atire forming mold according to the present invention, and shows a moldclamping state. In FIG. 1, an unvulcanized tire (not shown) is set insuch a manner that a tire axial direction is upside down, a right sidein FIG. 1 is an inner side in a tire diametrical direction, and a leftside in FIG. 1 is an outer side in the tire diametrical direction. FIG.2 is a plan view of a tread mold portion 1.

The tire forming mold (hereinafter, sometimes referred simply to as“forming mold”) is a segmented mold which is provided with a pair ofside mold portions 2 and 3 forming outer surfaces of side wall portionsof a tire, and a tread mold portion 1 fitted to outer sides in the tirediametrical direction of the side mold portions 2 and 3 at a time ofmold clamping, and forming an outer surface of a tread portion of thetire. A bead ring 4 is provided in an inner side in the tire diametricaldirection of the side mold portions 2 and 3, and is structured such thata bead portion of the tire can be fixed.

The tread mold portion 1 is constructed by a combination of sectors 5which are divided in a tire peripheral direction as shown in FIG. 2, andeach of the sectors 5 is structured such as to be displaceable in thetire diametrical direction. In the mold clamping state, the sectors 5get together and are connected as a circular ring shape by bringing endsurfaces into contact with each other. In a mold open state, the sectors5 displace to an outer side in the tire diametrical direction andseparate from the side mold portions 2 and 3. In the present embodiment,there is shown an example in which the tread mold portion 1 is dividedinto seven sections, and peripheral lengths of the sectors 5 areapproximately equal to each other, however, in the present invention,the number of division of the tread mold portion is not particularlylimited and the peripheral lengths of the sectors may be different fromeach other.

As a raw material of the tread mold portion 1, aluminum is exemplified.The aluminum is a concept including not only a pure aluminum rawmaterial but also an aluminum alloy, for example, there are listed upAl—Cu based, Al—Mg based, Al—Mg—Si based, Al—Zn—Mg based, Al—Mn based,and Al—Si based alloys. Further, as a raw material of the side moldportions 2 and 3, a steel material can be exemplified.

A container 6 is attached per sector 5 to an outer peripheral surfaceserving as a back surface side of the tread mold portion 1. Thecontainer 6 is attached to a lower surface of a side plate 7 structuredso as to freely move up and down, in such a manner as to be slidablealong the tire diametrical direction. A cone ring 8 is fitted to a rail9 provided in an outer slant face of the container 6, and is structuredsuch as to freely move up and down relatively with respect to the sideplate 7.

In the mold clamping state shown in FIG. 1, if the container 6 is movedto the outer side in the tire diametrical direction by moving up thecone ring 8, each of the sectors 5 displaces to the outer side in thetire diametrical direction so as to separate from the side mold portions2 and 3. If the side plate 7 and the container 6 are moved up further,the sector 5 and the side mold portion 3 are lifted up so as to give wayto the mold open state. The transition from the mold open state to themold clamping state can be achieved by carrying out the operationmentioned above inversely.

Although not being illustrated in the drawings, a rubber bag called abladder is installed in an inner portion of the forming mold. At a timeof the vulcanization forming, the outer surface of the tire is pressedto the inner surfaces of the tread mold portion 1 and the side moldportions 2 and 3, by inflating the bladder to the outer side in the tirediametrical direction. A rigid core can be used in place of the bladder,and the present invention can be applied both to a bladder vulcanizationand to a core vulcanization.

FIG. 3 is an enlarged view of a substantial part of the forming moldshown in FIG. 1, and shows a portion A in FIG. 1 in an enlarged manner.A rubber inflow portion 30 is provided in an inner surface of the sidemold portion 3. In the example in FIG. 3, two rubber inflow portions 30are provided. A rubber in an outer surface of the side wall portion ofthe unvulcanized tire is flowed into the rubber inflow portion 30 at atime of the vulcanization forming, and a protrusion portioncorresponding to a shape of the rubber inflow portion 30 is formed inthe outer surface of the tire after being vulcanized. Although detailswill be mentioned later, it is possible to form the tire in whichletters and lines having different colors are formed in the side wallportion, by buff treating a part of the protrusion portion. The actualrubber inflow portion 30 extends in a near direction and a far directionin FIG. 3, and the protrusion portion of the tire is formed in such amanner as to come to the shape of the formed letters and lines, in thecase of viewing from a tire axial direction.

A cross sectional shape of the rubber inflow portion 30 is constructedby a neck portion 30 b extending from an inflow port 30 a, and a headportion 30 c enlarged from the neck portion 30 b. It is preferable thata portion in which the neck portion 30 b and the head portion 30 c arecoupled is formed in such a manner as to be rounded and be smoothlyconnected. In the example in FIG. 3, the neck portion 30 b is formedsuch a shape as to be slightly narrowed toward the head portion 30 c.Further, the head portion 30 c is formed into an oval shape, however,the head portion 30 c is not limited to the circular shape.Specifically, the head portion 30 c may be formed into a quadrangularshape such as a trapezoid as shown in FIG. 4A. Further, the neck portion30 b may be parallel as shown in FIG. 4B, and any one of right and leftsides of the head portion 30 c may be larger than the neck portion 30 b.In this case, taking into consideration a working property at a time offorming the rubber inflow portion 30 in the forming mold, it ispreferable that the head portion 30 c is formed into a round shape. Inother words, in the case that the head portion 30 c is larger than theneck portion 30 b, it is preferable that the head portion 30 c is formedinto a round shape, since a cutting work by an end mill or the likebecomes hard if an angular portion exists in the head portion 30 c.

FIG. 5 is a tire meridian cross sectional view schematically showing anexample of the pneumatic tire according to the present embodiment. FIG.6 is a substantial part cross sectional view showing the substantialpart in an enlarged manner. The pneumatic tire is a radial tire which isprovided with a pair of bead portions 10, a side wall portion 11extending to an outer side in the tire diametrical direction from eachof the bead portions 10, a tread portion 12 connected to an outerperipheral end of each of the side wall portions 11, and a carcass ply13 arranged in such a manner as to be bridged between a pair of beadportions 10.

The bead portion 10 is provided with an annular bead core 10 a which isformed by rubber coating a convergence body such as a steel wire, and anannular bead filler 10 b which is positioned in an outer side in a tirediametrical direction of the bead core 10 a and is made of a hard rubberhaving a triangular cross sectional shape. The carcass ply 13 is woundup in such a manner as to pinch the bead core 10 a and the bead filler10 b so as to be locked in its end portion, and an inner liner rubberlayer 14 for holding a pneumatic pressure is arranged in an inner sidethereof. In the present embodiment, there is shown an example in whichone carcass ply 13 is arranged, however, a plurality of carcass pliesmay be arranged so as to be laminated.

A belt layer 15 and a belt reinforcing layer 16 are arranged in an outerside of the carcass play 13 in the tread portion 12, and a tread rubberlayer 17 is arranged in an outer side thereof. A rim protector 18 cominginto contact with a rim flange at a time of being installed to a vehicleis arranged in an outer side of the carcass ply 13 in the bead portion10. A side rubber layer 19 is arranged in an outer side of the carcassply 13 in the side wall portion 11. For these rubber layers, a carbonblack having a high reinforcing performance is generally used as filler,and they take on a black color.

A white rubber layer 20 (corresponding to the different color rubberlayer) taking on a white color is arranged in the side wall portion 11so as to be adjacent to an outer side of the side rubber layer 19. Anouter side surface of the white rubber layer 20 is coated by a blackthin cover rubber 21 (corresponding to the cover rubber layer), and awhite letter or line is formed by grinding it so as to partly expose thewhite rubber layer 20. The white rubber layer 20 is not necessarilyarranged in the side wall portions 11 in both sides, but is arrangedonly in a side (a right side in FIG. 5) serving as an outer side of thevehicle at a time of being installed to the vehicle in the presentembodiment.

A rubber composition for forming the white rubber layer 20 is known, anda conventionally known rubber composition can be used without beinglimited. The carbon black is not used as the reinforcing material in thewhite rubber layer 20, and a metal oxide, for example, an alumina, amagnesia, a silica or the like is substituted. The white rubber layer 20is softer and lower in rigidity than the side rubber layer 19, and arubber hardness (a rubber hardness measured according to a durometerhardness test (type A) of JIS K6253) thereof is, for example, between45° and 72°.

A method of vulcanization forming the unvulcanized tire by using thetire forming mold mentioned above, and forming the tire in which thewhite letters and lines are formed in the side wall portion 11 is asfollows. FIGS. 7A to 7C show a state of forming the tire. FIG. 7A showsa state of the tire before being vulcanization formed. As shown in thedrawing, the white rubber layer 20 and the cover rubber 21 of the sidewall portion 11 are in a state in which they are laminated in the outerside of the side rubber layer 19, and the outer surface of the coverrubber 21 is formed into a substantially planer shape. Next, theunvulcanized tire is set in the forming mold and a mold clamping iscarried out. Next, the outer surface of the tread portion 12 is broughtinto contact with the inner peripheral surface of the tread mold portion1, as well as the outer surface of the side wall portion 11 of the tireis brought into contact with the inner surface of the side mold portion3 (or the side mold portion 2), by inflating the bladder. Further, theforming mold is heated and held at a predetermined vulcanizationtemperature, and the vulcanization forming is applied to theunvulcanized tire in the inner portion. At this time, the white rubberlayer 20 and the cover rubber 21 of the side wall portion 11 flow intothe rubber inflow portion 30 provided in the inner surface of the sidemold portion 3, as shown in FIG. 7B, and a protrusion portion 31corresponding to the shape of the rubber inflow portion 30 is formed inthe side wall portion 11. After the vulcanization forming, thevulcanized tire is picked up by opening the forming mold.

Finally, as shown in FIG. 7C, the tire in which the white letters andlines are formed in the side wall portion 11 can be formed by bufftreating a leading end portion of the protrusion portion 31 of thevulcanization formed tire. The buff treated surface is a position (shownby a broken line in FIG. 7C) which is formed by the neck portion 30 b ofthe rubber inflow portion 30, in the protrusion portion 31.

Examples

A description will be given below of an example specifically showing thestructure and the effect of the present invention. The tire in which thewhite letters are formed was manufactured by using the tire forming moldaccording to the present invention and the conventionally known tireforming mold, and was evaluated. The evaluation was done based onwhether or not the black cover rubber is left in the portion which comesto the white letter by right. Specifically, a size of the white rubbertire was set to 285/70R17, and one thousand of tires were manufactured.

FIG. 8 shows a shape of the rubber inflow portion of the used tireforming mold. As the tire forming mold according to the presentinvention, there were prepared tire forming molds respectively providedwith a rubber inflow portion in which the head portion is formed into atrapezoidal shape (example 1), a rubber inflow portion in which the headportion is formed into a quadrangular shape (example 2), and a rubberinflow portion in which the head portion is formed into an oval shape(example 3). In this case, in the rubber inflow portion according to theexample 1, it is preferable that the head portion is enlarged at anangle between 5° and 25° with respect to a direction which is verticalto a profile reference surface. If an angle of enlargement of the headportion is equal to or less than 5°, a volume of the head portion isinsufficient, a volume of the white rubber falls short and the blackcover rubber tends to be left. If the angle of enlargement of the headportion is equal to or more than 25°, there is generated such a problemthat a working tool interferes with the forming mold. Further, it ispreferable that the neck portion is narrowed at an angle between 10° and15° with respect to the direction which is perpendicular to the profilereference surface toward the head portion. The tires were formed by thetire forming molds according to the examples 1 to 3, however, the blackcover rubber was not left in the portion to be the white letter by rightin all the tires formed by the tire forming molds.

On the contrary, in the case of using a tire forming mold provided witha conventionally known rubber inflow port (comparative example 1), theblack cover rubber was left in the portion to be the white letter byright, in five tires of one thousand of formed tires. Further, in thecase of using a tire forming mold provided with a rubber inflow port(comparative example 2) in which the neck portion and the head portionare formed as the same magnitude, the black cover rubber was left in theportion to be the white letter by right, in three tires of one thousandof formed tires.

What is claimed is:
 1. A tire forming mold for vulcanization forming bybeing brought into contact with an outer surface of a tire which isprovided with a side rubber layer of a first color arranged in an outerside of a carcass ply of a side wall portion, a different color rubberlayer of a second color arranged in adjacent to an outer side of theside rubber layer, and a cover rubber layer of the first color arrangedin adjacent to an outer side of the different color rubber layer, thetire forming mold comprising: a rubber inflow portion for forming aprotrusion portion in an outer surface of the tire by inflowing thedifferent color rubber layer and the cover rubber layer, in the contactsurface with the tire, wherein a cross sectional shape of the rubberinflow portion is constructed by a neck portion extending from an inflowport, and a head portion enlarged from the neck portion.
 2. The tireforming mold according to claim 1, wherein the head portion is formedinto a round shape.
 3. A tire forming method of vulcanization forming byarranging a side rubber layer of a first color in an outer side of acarcass ply of a side wall portion, arranging a different color rubberlayer of a second color in adjacent to an outer side of the side rubberlayer, and bringing an outer surface of a tire in which the cover rubberlayer of the first color is arranged in adjacent to an outer side of thedifferent color rubber layer into contact with a tire forming mold,wherein the tire forming mold is provided with a rubber inflow portionin a contact surface with the tire, and a cross sectional shape of therubber inflow portion is constructed by a neck portion extending from aninflow port, and a head portion enlarged from the neck portion, and aprotrusion portion is formed in the outer surface of the tire byinflowing the different color rubber layer and the cover rubber layerinto the rubber inflow portion.